Most existing water jets in spas or "hot tubs" are fixed, i.e. their direction of spray remains constant. One jet is known which uses a flexible pipe for a nozzle. This causes a spray which flops about unpredictably due to hydraulic forces in much the same way as a loose water hose. This flexible pipe jet is marketed by Watkins Hot Springs Co. under the trademark MOTO JET.
U.S. Pat. No. 4,339,833 of G. Mandell teaches a reciprocating hydro-massage apparatus where the flow moves up and down on a helical track screw. The whole apparatus, pipes, impeller and all, moves up and down the screw. Such an apparatus is prone to failure due to corrosion of the drive screw and incorporates an electric motor which requires elaborate precautions to prevent shock in the aquatic environment of spas. Another embodiment uses a mechanical impeller whose weight is likely to damage the track of the screw. The Mandell mechanism, while reciprocating, does not impart an arcuate motion to the spray and uses only one nozzle.
There exists a need for water jets which move their spray in a fixed pattern up and down the user's spine in the manner of a human masseuse. Specifically, it is desired to provide a spa jet system which "massages" the entire back of a user in a systematic manner which is conducive to relaxation and as therapy for chronic back pain.